If I'm right:
Terra + MX's heart (+ Eraqus' heart) = Xehanort (+ Eraqus heartless / Xehanort's Guardian)
When he became a nobody, he's made out of Terra's body and Terra's Soul, so Aqua's armor told Xemnas where Ven is because she thought this is the true Terra and wanted him to safe Ven or something like this :/
Terra + MX's heart (+ Eraqus' heart) = Xehanort (+ Eraqus heartless / Xehanort's Guardian)
When he became a nobody, he's made out of Terra's body and Terra's Soul, so Aqua's armor told Xemnas where Ven is because she thought this is the true Terra and wanted him to safe Ven or something like this :/